This invention relates to the copolymerization of mono-1-olefin monomers, such as ethylene, with at least one higher alpha-olefin comonomer.
It is well known that mono-1-olefins, such as ethylene, can be polymerized with catalyst systems employing vanadium, chromium, or other metals on supports such as alumina, silica, aluminophosphate, titania, zirconia, magnesia and other refractory metals. Initially, such catalyst systems were used to form primarily homopolymers of ethylene. It soon developed, however, that many applications required polymers having more impact resistance than ethylene homopolymers. Consequently, polymers were developed having short chain branching, like the more flexible free radical polymerized ethylene polymers, by adding comonomers such as propylene, butene, hexene and other higher alpha-olefins which were copolymerized with ethylene to provide resins tailored to specific end uses. These polymers, and processes to make such polymers, were improved in order to more efficiently incorporate comonomers into the polymer to produce linear, low-density copolymers having high impact resistance, especially when made into films.
Unfortunately, during polymerization processes to produce these improved copolymers, the heat transfer coefficient of the polymerization reactor can be severely reduced. Loss, or decrease, of the heat transfer coefficient can result in a loss of cooling efficiency of the reactor. During the polymerization reaction, polymer product can coat, or plate out on, the reactor walls and start foul conditions in the reactor. This coating phenomenon can cause a loss of cooling efficiency, which is indicated by a decrease of the heat transfer coefficient in the reactor. A significant loss of reactor cooling efficiency creates polymer production limits on the reactor. Generally, once foul conditions begin, the condition is very difficult to reverse and fouling continues at an ever increasing rate. Eventually, the reactor can enter a condition known as "full foul", which can result when a significant build-up of polymer plates out on the reactor walls. In fact, fouling conditions can be so bad that the entire reactor can become completely plugged with solid polymer. Correction of such types of foul conditions usually requires a complete shut-down of the reactor and cleaning of the reactor walls. A reactor shut-down to correct fouling conditions can take up to several days, depending on the severity of the fouling, and can result in a significant loss of polymer production and can have a serious detrimental economic impact. Cleaning the reactor walls can restore the heat transfer coefficient to original operating conditions and can improve the cooling efficiency of the reactor.